1. Field of the Invention
The present invention generally relates to an automatic sensor-calibration method, and more particularly, to an automatic sensor-calibration method in which a state change of a sensor, caused by aging characteristics or contamination of the sensor, is sensed by a sensor input unit to adjust, according to the sensed state change of the sensor, a slice level used as a criterion for a light receiving device to determine whether a medium exists, or the slice level is adjusted according to the sensed state change of the sensor and a current level of a light emitting device is adjusted when the slice level reaches a preset absolute slice level, or when contamination of the sensor is removed, the current level of the light emitting device is reduced to a minimum step, the slice level is reset, and then the current level of the light emitting device is adjusted again based on the reset slice level, thereby preventing malfunction of the sensor.
2. Description of the Related Art
Automated Teller Machines (ATMs) are automated devices capable of providing basic financial services such as withdrawal and deposit without bank tellers regardless of time and space. The ATMs are configured such that customers themselves can do transaction such as withdrawal or deposit of cash by using media like cards or bankbooks.
Since most companies have adopted a 5-day workweek, most people use ATMs or Cash Dispensers (CDs) instead of directly going to the bank, expanding installation of ATMs and increasing the number of ATMs installed. At present, ATMs having additional functions as well as main functions are under consideration and new ATMs are being developed to improve competitiveness of banks and to satisfy customers' demands.
The ATM includes numerous sensors by which the ATM can control a flow of money. FIG. 1 illustrates an example of modules of a sensor 100 of an ATM.
As illustrated in FIG. 1, the sensor 100 includes a light emitting device 110, such as a light emitting diode (LED), which generates a light signal with an electric current adjusted by variable resistors, and a light receiving device 120 which receives the generated light signal, in which the electric-current adjustment for the light emitting device 110 is performed by a Digital-to-Analog Converter (DAC). By having the structure as illustrated in FIG. 1, the sensor 100 of the ATM can sense a flow of a medium such as money or a cash card between the light emitting device 110 and the light receiving device 120.
In other words, it is determined that a medium such as money does not exist when the light receiving device 120 senses light of an amount greater than a predetermined amount. When the light receiving device 120 senses light of an amount less than the predetermined amount, it is determined that a medium exists between the light emitting device 110 and the light receiving device 120. FIG. 2 is a graph illustrating a criterion used for a conventional sensor to determine existence of a medium.
As illustrated in FIG. 2, for a slice level of 6V which is used as a criterion to determine existence of a medium, when a voltage of a light emitting device is sensed to be 6.1-12V, it is determined that the medium exists between the light emitting device and a light receiving device. When the voltage of the light emitting device is sensed to be 0-5.99V, it is determined that the medium does not exist between the light emitting device and the light receiving device.
However, the slice level of the sensor is a fixed absolute reference value, causing undesired malfunction of the sensor. For example, when light emitted from the light emitting device is lower than a slice level due to deterioration of the sensor used for a long period of time or due to settlement of dust or foreign substances on the light emitting device, the ATM determines that the sensor senses a medium even if the medium does not actually exist between the light emitting device and the light receiving device, resulting in malfunction of the sensor. Such malfunction of the sensor increases the number of operations of the ATM, degrading the efficiency of the ATM.
To solve those problems, methods for changing a slice level according to a state change of a sensor have been suggested. These methods, however, merely increase the slice level when the sensor is polluted by contaminants. Thus, when the contaminants are removed by an operator or through movement of a medium existing between the light emitting device and the light receiving device, determination of whether the sensor senses the medium is performed based on the increased slice level. As a result, the ATM determines that the sensor senses no medium even if the medium actually exists between the light emitting device and the light receiving device.